The only target of neutralizing anti-HIV-1 antibodies is the envelope (Env) spike, a heterotrimer of gp120 and gp41 subunits. Single cell-based antibody cloning techniques have recently uncovered a large number of antibodies that can potently neutralize highly diverse HIV-1 variants by targeting Env (Klein et al., Science 341, 1199 (2013)). When transferred passively, broadly neutralizing antibodies (bNAbs) can prevent infection by HIV-1 or SHIV in humanized mice and macaques, respectively. Moreover, combinations of bNAbs can also suppress established HIV-1 and SHIV infections (Klein et al., Nature 492, 118 (2012); Barouch et al., Nature 503, 224 (2013); Shingai et al., Nature 503, 277 (2013)).
Most of the bNAbs characterized to date target one of four major sites of vulnerability on HIV-1 Env: on gp120, the CD4 binding site, the V2 loop, and the base of the V3 loop, and on gp41, the membrane proximal region (Klein et al., Science 341, 1199 (2013); Burton et al., Science 337, 183 (2012); Mascola et al., Immunological Reviews 254, 225 (2013)). 8ANC195 is among a small group of bNAbs that does not appear to target any of these sites. Although only two of the B cells originally isolated from the 8ANC195 donor, an HIV-1 elite controller, belonged to the 8ANC195 clone, the antibodies produced by this clone complemented the neutralizing activity of antibodies produced by a more expanded. B cell clone that targeted the CD4 binding site (Scheid et al., Science 333, 1633 (2011)).
8ANC1.95 is classified as a bNAb because it neutralized 66% of viruses in a diverse viral panel. (Scheid et al., Science 333, 1633 (2011)). Like other anti-HIV-1 bNAbs, 8ANC195 is highly somatically mutated, including insertions and deletions in the complementarily determining regions (CDRs) and framework regions (FWRs) of its heavy chain (HC) and light chain (LC). Although initial efforts to map the 8ANC195 epitope were unsuccessful (Ibid.) computational analyses of neutralization data predicted that intact potential N-linked glycosylation sites (PNGSs) at positions 234gp120 and 276gp120 were essential for its activity. These predictions were confirmed by evaluating the neutralization potency of 8ANC195 against mutant HIV-1 strains in vitro and in vivo (West, Jr. et al., Proceedings of the National Academy of Sciences of the United States of America 110, 10598 (2013); Chuang et al. Journal of Virology 87, 10047 (2013)). However, the precise 8ANC195 epitope on HIV-1 Env has heretofore remained elusive.